Arzenti deals with the sleeving of corroded or damaged tubes of steam generators of nuclear reactors. The tubes are typically U-shaped and are sealed in a tube sheet. A channel head extends from the periphery of the tube sheet and the damaged tubes are accessible from within the channel head which may be entered through a manway. When a reactor plant is in operation, the channel head conducts the coolant. The environment within the channel head is radioactive and access to the damaged tubes is available only through this radioactive environment. Each damaged tube is sleeved by inserting a sleeving assembly including a sleeve blank mounted on a mandrel into the damaged tube. After the sleeve blank is inserted in the tube the mandrel must be removed. The mandrel varies widely in cross-sectional diameter and in surface contour along its length.
Arzenti discloses a tool and a method for carrying out the sleeving by remote control thus minimizing the exposure of personnel to radioactivity. This tool includes gripper assemblies for holding and advancing the sleeving assembly when the sleeve is being inserted and for holding and retracting the mandrel after the sleeve blank is fully inserted.
In the use of the Arzenti tool and in practicing the method which Arzenti teaches, it is indispensable that the sleeving assembly, and particularly the sleeve blank, be precisely centered coaxially with the tube being sleeved. It is also necessary that the gripper assemblies which deliver the sleeve blank into the tube be capable of exerting the necessary force at the joint between the sleeve blank and the tube to effect the delivery. In other words, the gripper assembly which advances the sleeve blank into the tube must grasp the sleeve blank so firmly that the full advancing force initially exerted on the gripper assembly and through it on the sleeve blank is transferred to the sleeve blank as the force which advances it into the tube. The advancing force should not be dissipated in part in sliding the gripper along the sleeve blank. The diameters of the sleeve blanks which are in use vary over a wide range. The gripper assembly should be compatible with sleeves of different diameters within this range. The gripper assembly should have a gripping mechanism which conforms to the surface of an elongated object whose cross-sectional dimension varies from point to point along its length over a wide range.
It is an object of this invention to provide a gripper assembly which shall meet the above requirements; namely a gripper assembly in whose use the object being gripped shall be precisely centered with respect to the target towards which it is being advanced, which shall grip the object so firmly that the advancing force exerted between the gripper and the object shall be transferred to the object to enable the object to exert whatever force is necessary to enable the object to reach its destination, which shall be capable of gripping objects over a wide range of surface contours or cross-sectional dimensions, which shall have a gripping member capable of conforming to the surface of an object having an irregular surface, and which shall operate rapidly to engage or disengage the surface.